# WebForms AsyncUpload Overview

This article gives a quick overview of the **RadAsyncUpload** control and shows the steps to declare it. We also describe some of the major features of **RadAsyncUpload** that was introduced in Q1 2010 with [UI for ASP.NET AJAX 2010.1.309](https://www.telerik.com/support/whats-new/aspnet-ajax/release-history/ui-for-asp-net-ajax-2010-1309).

**RadAsyncUpload** looks like the regular **RadUpload** control but offers an *asynchronous upload* capability. The upload process requires that the files are uploaded to a custom handler and not to the hosting page. The uploaded files are stored in a temporary location *until a postback* occurs. The temporary files are deleted after a set amount of time defined by the [TemporaryFileExpiration](https://docs.telerik.com/devtools/aspnet-ajax/api/server/Telerik.Web.UI/RadAsyncUpload#temporaryfileexpiration) property. The default value is 4 hours.

![WebForms ajaxPanel Overview](https://www.telerik.com/products/aspnet-ajax/documentation/assets/08392334688dced6d2c4f4ae05e52405/asyncupload-overview.png "WebForms ajaxPanel Overview")

## Get started with the RadAsyncUpload

> caption To create a basic `RadAsyncUpload`:

1. Ensure you have a script manager on the page (use \<asp:ScriptManager> tag to declare one).
2. Use the \<telerik:RadAsyncUpload> tag to declare the control and specify the file upload folder by setting the TargetFolder property.

> caption Get started with the async upload declaration and enabling some of its features

```ASP.NET
<telerik:RadAsyncUpload RenderMode="Lightweight" ID="RadAsyncUpload1" TargetFolder="Uploads" AllowedFileExtensions=".jpeg,.jpg,.png,.doc,.docx,.xls,.xlsx" runat="server"></telerik:RadAsyncUpload>
```

For more information on setting up the environment see the [Install Telerik UI for ASP.NET AJAX using MSI installer](https://www.telerik.com/products/aspnet-ajax/documentation/getting-started/installation/install-using-msi) article.

## Temporary Files

**RadAsyncUpload** relies on saving temporary files. When posted, files are saved to the designated temp folder (**App_Data/RadUploadTemp** by default) with unique names. Once a postback occurs, **RadAsyncUpload** fires the **OnFileUploaded** event for each file. The target file is passed as part of the arguments to the event and can be set as either valid (default) or invalid. After the events fire, all files marked as valid are automatically saved to the **TargetFolder** if it’s set.

Finally, all processed temporary files are deleted. Temporary files are also deleted after a set amount of time defined by the **TemporaryFileExpiration** property.

> note With the release of Q1 2011 SP2, **RadAsyncUpload** supports setting the temporary folder globally in the appSettings section of the web.config.
> **< add key="Telerik.AsyncUpload.TemporaryFolder" value="\[path_to_the_temporary_folder]" />**
> The path can be relative or absolute.

## Validation

Validation for **RadAsyncUpload** differs from validation in **RadUpload** as now it is possible to validate the file size on the client using the **File API** upload module. If the validation fails, **RadAsyncUpload** will fire **OnClientValidationFailed**.

## Upload Module

**RadAsyncUpload** uses the **File API** upload module, which is natively supported by all modern browsers.

> note As of **2026 Q1 SP2**, the legacy **IFrame**, **Silverlight** and **Flash** modules have been removed from the source code. This change improves the compatibility with modern browsers and hardens the security of the RadAsyncUpload control.

## Web Farms

In web farms, each server will need to use the *same MachineKey* that **RadAsyncUpload** uses for encryption. Most web farms should already have their MachineKeys synchronized as this is the recommended approach for web farm deployment. For more information see the [How to integrate RadControls for ASP.NET AJAX in a WebFarm or WebGarden scenario](https://www.telerik.com/blogs/integrate-radcontrols-for-asp.net-ajax-in-a-webfarm-or-webgarden) blog post.

## Maximum File Size

One of the benefits of RadAsyncUpload is that it allows you to upload files bigger than 2GB. See [Uploading Large Files](https://www.telerik.com/products/aspnet-ajax/documentation/controls/asyncupload/functionality/uploading-large-files) for more details.

## See Also

* [Install Telerik UI for ASP.NET AJAX using MSI installer](https://www.telerik.com/products/aspnet-ajax/documentation/getting-started/installation/install-using-msi)

* [Getting Started](https://www.telerik.com/products/aspnet-ajax/documentation/controls/asyncupload/getting-started)

* [Migrating from RadUpload for ASP.NET AJAX to RadAsyncUpload](https://www.telerik.com/products/aspnet-ajax/documentation/controls/asyncupload/migrating-from-radupload-for-asp.net-ajax-to-radasyncupload)

* [RadAsyncUpload vs. RadUpload for ASP.NET AJAX](https://www.telerik.com/products/aspnet-ajax/documentation/controls/asyncupload/radasyncupload-vs-radupload)

* [RadAsyncUpload Modules](https://www.telerik.com/products/aspnet-ajax/documentation/controls/asyncupload/upload-modules)

* [Uploading Large Files](https://www.telerik.com/products/aspnet-ajax/documentation/controls/asyncupload/functionality/uploading-large-files)

* [Online Demos](https://demos.telerik.com/aspnet-ajax/asyncupload/examples/overview/defaultcs.aspx)

* [ASP.NET AJAX Upload (Async)](https://www.telerik.com/products/aspnet-ajax/asyncupload.aspx)